1. Field of the Invention
The present invention relates to a method of switching operating systems (hereinafter simply referred to as "OS") for a data processing system and, more particularly, to an OS switching method for a data processing system in which one of the operating systems stored in the auxiliary storage is selectively loaded into the main storage depending on the usage of the data processing system so that it is operated for many purposes.
2. Description of the Prior Art
The recent advances in semiconductor technology have brought increased use of office automation facilities such as word processors and personal computers using sophisticated microprocessors integrated in a tiny chip. As for the computerization of the business office, there are generally installed several on-line terminal devices connected to a host computer, and other office automation facilities such as word processors as mentioned above are used for local data processing in each office independently of the on-line computer system. However, in order to avoid the multiple installation of similar hardware devices including on-line terminals, word processors and personal computers for much efficient use of the office, it is desirable for an on-line terminal device to have multi-purpose functions including capabilities of a word processor and personal computer for dealing with local data processing.
In order for the data processing system to perform such multi-functional operations, it is necessary to replace the operating system in the main storage for each purpose. For example, an operating system EMP (Emulation Program*) is used when a terminal device is used for real time data processing in a interactive mode, MS-DOS (trademark of Microsoft Inc., U.S.A.) is used when a terminal device is used as a personal computer, WPS (Word Processing System*) including the character conversion function and learning function is used when it is used as a word processor, or BTOS (Business Terminal Operating System*) is used when it is used as an intelligent terminal for entering local data into the data base of the host computer. (Note: Operating systems marked by "*" are products of Hitachi Ltd., Japan)
Conventionally, the operating system stored in the auxiliary storage is loaded to the main storage by the Initial Program Loader (IPL). Accordingly, when the system is intended to operate under one of several operating systems stored in the auxiliary storage depending on each usage, the overall contents of the main storage are renewed each time in such a way that the operator resets the system, activates the IPL, and specifies through the keyboard the operation system to be loaded, so that the system starts with the execution of IPL. After the operating system has been loaded to the main storage, data sets associated with the OS such as dictionary data and data for character generation are also loaded from the auxiliary storage to the main storage.
According to the conventional method for dealing with operating systems, a data set needed by a new operating system is automatically loaded from the auxiliary storage to the main storage even if it already resides in the main storage as an accompaniment of the previous operating system. In addition, even though the main storage has been checked at the loading of the previous operating system, it is checked again in the new OS loading operation beginning with IPL. That is, the conventional method involves unnecessary steps of start-up procedure each time the operating system is replaced. The operator's system reset action abruptly terminates a job in execution, resulting possibly in an improper abortion of the processing.